These types of fluid valves are often referred to as spool valves because they incorporate a spool-shaped armature or piston which moves endwise in the valve housing and has a number of grooves and lands at its periphery for variously connecting the main passages of the valve.
Such spool valves are especially useful in valving hydraulic liquids such as hydraulic oil, but are also useful in valving gaseous fluids. Where herein reference is made to fluids or hydraulic oils or liquids, it should be understood that the language may also be extended to compressible or elastic gaseous fluids.
Valving hydraulic oils for operating motors such as hydraulic cylinders with moving pistons, presents a wide variety of problems under widely varying circumstances. Fluid valves available in the past have not provided the desired fine control under certain circumstances as may be desired. Also, under adverse conditions such as extremely cold temperatures, fluid-operated valves have had a propensity to be very sluggish, or to not operate at all due to the viscosity of the hydraulic oils.
Other problems encountered in spool valves have been the noise with which they operate, the adverse conditions created in the event of a spring breaking, and the unnecessary complicated nature of the operating mechanisms.
Prior patents illustrate various forms of spool valves, none of which addresses itself to solving such problems and providing the advantages found in the present invention. Such prior patents include Hennells U.S. Pat. No. 3,418,002; Yoshino 4,014,509; Rothrock 3,530,895; Raymond 3,522,817; Kast 3,433,021; Knowles 3,552,442; Mercier 3,563,272; Beckett 3,565,115; Christensen 3,576,194; Kirstein 3,633,871; Roth 3,768,518; Johnson 3,990,477; Kutik 3,508,584; and Hague 3,773,083.